The flexible display device is a display device of which the display substrate can be bent, and includes a flexible organic electroluminescent display device (OLED), a flexible electrophoretic display device (EPD), a flexible liquid crystal display device (LCD) and other types.
Different from conventional display device, a flexible display substrate (an array substrate, and a color filter substrate or the like) is used in the flexible display device. The base of the flexible display substrate can be made of bendable flexible material such as plastic, so that the display device can be bent. However, certain structures (e.g. thin film transistors, etc.) on the flexible display substrate have poor flexibility. They are easily to be failed or worn when the flexible display device is bending and cause the flexible display substrate damaged or degraded (such structures may be called the “fragile structure”). For example, when the active region of the thin film transistor is worn, thus generated signal will drift and defect will occur in display.
Meanwhile, even in the case where damage does not occur, deformation of some display structure may also cause display defects. For example, in the flexible liquid crystal display device, if the display area of the pixel cell is deformed, the orientation of corresponding liquid crystal molecules may be changed undesirably under the deformation stress, leading to display errors. For this, the existing flexible liquid crystal display device can withstand comparative low deformation under the premise of normal display.
To solve the above problem, the prior art mainly uses the following two methods:
One method is to use a flexible material which is easy to bend in various display structures in the flexible display devices, for example, using an oxide semiconductor (such as gallium indium zinc oxide, IGZO), or organic semiconductor (such as phthalocyanine copper, PcCu) instead of the silicon-based semiconductor material in the active region of the thin film transistor (TFT). However, not all of the display structures may be made from material with good flexibility, which limits the selection for material; and even if there are substitute materials, they may not achieve the performance, cost, and so on of existing materials, and the utility of substitute materials may result in degraded performance and increased costs of the flexible display device. Moreover, if substitute material is used, the structure, manufacturing process of the flexible display substrate will be changed significantly, and may not be obtained through existing processes and equipment.
The second method is to encapsulate various display structures on the flexible display substrate using an elastic material layer, to protect these structures from damage. However, while protecting the fragile structure, the elastic material layer may also limit the deformation of the flexible display substrate, resulting in a reduced deformation ability of the flexible display device.
Meanwhile, according to the above two methods, when the deformation occurs, the deformation extent (or curvature) of each part of the flexible display substrate are the same or similar; therefore neither of the two methods can overcome the undesirable display caused by deformation without damage (e.g. undesirable display due to undesirable orientation change in the liquid crystal material).